#include <stdint.h>

typedef struct {
    uint32_t state[4];
    uint32_t count[2];
    unsigned char buffer[64];
} MD5_CTX;

void MD5_Init(MD5_CTX *ctx);
void MD5_Update(MD5_CTX *ctx, const unsigned char *input, unsigned int inputLen);
void MD5_Final(MD5_CTX *ctx, unsigned char *digest);

/* MD5 basic functions */
#define MD5_F(x, y, z) (((x) & (y)) | ((~x) & (z)))
#define MD5_G(x, y, z) (((x) & (z)) | ((y) & (~z)))
#define MD5_H(x, y, z) ((x) ^ (y) ^ (z))
#define MD5_I(x, y, z) ((y) ^ ((x) | (~z)))

/* MD5 transformations */
#define MD5_FF(a, b, c, d, x, s, ac) { \
    (a) += MD5_F((b), (c), (d)) + (x) + (uint32_t)(ac); \
    (a) = ROTATE_LEFT((a), (s)); \
    (a) += (b); \
}
#define MD5_GG(a, b, c, d, x, s, ac) { \
    (a) += MD5_G((b), (c), (d)) + (x) + (uint32_t)(ac); \
    (a) = ROTATE_LEFT((a), (s)); \
    (a) += (b); \
}
#define MD5_HH(a, b, c, d, x, s, ac) { \
    (a) += MD5_H((b), (c), (d)) + (x) + (uint32_t)(ac); \
    (a) = ROTATE_LEFT((a), (s)); \
    (a) += (b); \
}
#define MD5_II(a, b, c, d, x, s, ac) { \
    (a) += MD5_I((b), (c), (d)) + (x) + (uint32_t)(ac); \
    (a) = ROTATE_LEFT((a), (s)); \
    (a) += (b); \
}

/* MD5 constants */
static const unsigned char PADDING[64] = {
    0x80, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
    0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
    0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
    0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00
};

/* MD5 initialization. Begins an MD5 operation, writing a new context. */
void MD5_Init(MD5_CTX *ctx) {
    ctx->count[0] = ctx->count[1] = 0;
    ctx->state[0] = 0x67452301;
    ctx->state[1] = 0xefcdab89;
    ctx->state[2] = 0x98badcfe;
    ctx->state[3] = 0x10325476;
}

/* MD5 block update operation. Continues an MD5 message-digest operation, processing another message block. */
void MD5_Update(MD5_CTX *ctx, const unsigned char *input, unsigned int inputLen) {
    unsigned int i, index, partLen;

    index = (unsigned int)((ctx->count[0] >> 3) & 0x3F);

    if ((ctx->count[0] += ((uint32_t)inputLen << 3)) < ((uint32_t)inputLen << 3)) {
        ctx->count[1]++;
    }
    ctx->count[1] += ((uint32_t)inputLen >> 29);

    partLen = 64 - index;

    if (inputLen >= partLen) {
        memcpy(&ctx->buffer[index], input, partLen);
        MD5_Transform(ctx->state, ctx->buffer);

        for (i = partLen; i + 63 < inputLen; i += 64) {
            MD5_Transform(ctx->state, &input[i]);
        }

        index = 0;
    } else {
        i = 0;
    }

    memcpy(&ctx->buffer[index], &input[i], inputLen - i);
}

/* MD5 finalization. Ends an MD5 message-digest operation, writing the message digest and zeroizing the context. */
void MD5_Final(MD5_CTX *ctx, unsigned char *digest) {
    unsigned char bits[8];
    unsigned int index, padLen;

    MD5_Encode(bits, ctx->count, 8);

    index = (unsigned int)((ctx->count[0] >> 3) & 0x3f);
    padLen = (index < 56) ? (56 - index) : (120 - index);

    MD5_Update(ctx, PADDING, padLen);
    MD5_Update(ctx, bits, 8);

    MD5_Encode(digest, ctx->state, 16);

    memset(ctx, 0, sizeof(*ctx));
}

/* MD5 basic transformation. Transforms state based on block. */
void MD5_Transform(uint32_t state[4], const unsigned char block[64]) {
    uint32_t a = state[0], b = state[1], c = state[2], d = state[3], x[16];

    MD5_Decode(x, block, 64);

    /* Round 1 */
    MD5_FF(a, b, c, d, x[0], 7, 0xd76aa478);
    MD5_FF(d, a, b, c, x[1], 12, 0xe8c7b756);
    MD5_FF(c, d, a, b, x[2], 17, 0x242070db);
    MD5_FF(b, c, d, a, x[3], 22, 0xc1bdceee);
    MD5_FF(a, b, c, d, x[4], 7, 0xf57c0faf);
    MD5_FF(d, a, b, c, x[5], 12, 0x4787c62a);
    MD5_FF(c, d, a, b, x[6], 17, 0xa8304613);
    MD5_FF(b, c, d, a, x[7], 22, 0xfd469501);
    MD5_FF(a, b, c, d, x[8], 7, 0x698098d8);
    MD5_FF(d, a, b, c, x[9], 12, 0x8b44f7af);
    MD5_FF(c, d, a, b, x[10], 17, 0xffff5bb1);
    MD5_FF(b, c, d, a, x[11], 22, 0x895cd7be);
    MD5_FF(a, b, c, d, x[12], 7, 0x6b901122);
    MD5_FF(d, a, b, c, x[13], 12, 0xfd987193);
    MD5_FF(c, d, a, b, x[14], 17, 0xa679438e);
    MD5_FF(b, c, d, a, x[15], 22, 0x49b40821);

    /* Round 2 */
    MD5_GG(a, b, c, d, x[1], 5, 0xf61e2562);
    MD5_GG(d, a, b, c, x[6], 9, 0xc040b340);
    MD5_GG(c, d, a, b, x[11], 14, 0x265e5a51);
    MD5_GG(b, c, d, a, x[0], 20, 0xe9b6c7aa);
    MD5_GG(a, b, c, d, x[5], 5, 0xd62f105d);
    MD5_GG(d, a, b, c, x[10], 9, 0x02441453);
    MD5_GG(c, d, a, b, x[15], 14, 0xd8a1e681);
    MD5_GG(b, c, d, a, x[4], 20, 0xe7d3fbc8);
    MD5_GG(a, b, c, d, x[9], 5, 0x21e1cde6);
    MD5_GG(d, a, b, c, x[14], 9, 0xc33707d6);
    MD5_GG(c, d, a, b, x[3], 14, 0xf4d50d87);
    MD5_GG(b, c, d, a, x[8], 20, 0x455a14ed);
    MD5_GG(a, b, c, d, x[13], 5, 0xa9e3e905);
    MD5_GG(d, a, b, c, x[2], 9, 0xfcefa3f8);
    MD5_GG(c, d, a, b, x[7], 14, 0x676f02d9);
    MD5_GG(b, c, d, a, x[12], 20, 0x8d2a4c8a);

    /* Round 3 */
    MD5_HH(a, b, c, d, x[5], 4, 0xfffa3942);
    MD5_HH(d, a, b, c, x[8], 11, 0x8771f681);
    MD5_HH(c, d, a, b, x[11], 16, 0x6d9d6122);
    MD5_HH(b, c, d, a, x[14], 23, 0xfde5380c);
    MD5_HH(a, b, c, d, x[1], 4, 0xa4beea44);
    MD5_HH(d, a, b, c, x[4], 11, 0x4bdecfa9);
    MD5_HH(c, d, a, b, x[7], 16, 0xf6bb4b60);
    MD5_HH(b, c, d, a, x[10], 23, 0xbebfbc70);
    MD5_HH(a, b, c, d, x[13], 4, 0x289b7ec6);
    MD5_HH(d, a, b, c, x[0], 11, 0xeaa127fa);
    MD5_HH(c, d, a, b, x[3], 16, 0xd4ef3085);
    MD5_HH(b, c, d, a, x[6], 23, 0x04881d05);
    MD5_HH(a, b, c, d, x[9], 4, 0xd9d4d039);
    MD5_HH(d, a, b, c, x[12], 11, 0xe6db99e5);
    MD5_HH(c, d, a, b, x[15], 16, 0x1fa27cf8);
    MD5_HH(b, c, d, a, x[2], 23, 0xc4ac5665);

    /* Round 4 */
    MD5_II(a, b, c, d, x[0], 6, 0xf4292244);
    MD5_II(d, a, b, c, x[7], 10, 0x432aff97);
    MD5_II(c, d, a, b, x[14], 15, 0xab9423a7);
    MD5_II(b, c, d, a, x[5], 21, 0xfc93a039);
    MD5_II(a, b, c, d, x[12], 6, 0x655b59c3);
    MD5_II(d, a, b, c, x[3], 10, 0x8f0ccc92);
    MD5_II(c, d, a, b, x[10], 15, 0xffeff47d);
    MD5_II(b, c, d, a, x[1], 21, 0x85845dd1);
    MD5_II(a, b, c, d, x[8], 6, 0x6fa87e4f);
    MD5_II(d, a, b, c, x[15], 10, 0xfe2ce6e0);
    MD5_II(c, d, a, b, x[6], 15, 0xa3014314);
    MD5_II(b, c, d, a, x[13], 21, 0x4e0811a1);
    MD5_II(a, b, c, d, x[4], 6, 0xf7537e82);
    MD5_II(d, a, b, c, x[11], 10, 0xbd3af235);
    MD5_II(c, d, a, b, x[2], 15, 0x2ad7d2bb);
    MD5_II(b, c, d, a, x[9], 21, 0xeb86d391);

    state[0] += a;
    state[1] += b;
    state[2] += c;
    state[3] += d;

    memset(x, 0, sizeof(x));
}

/* Encodes input (uint32_t) into output (unsigned char). Assumes len is a multiple of 4. */
void MD5_Encode(unsigned char *output, const uint32_t *input, unsigned int len) {
    unsigned int i, j;

    for (i = 0, j = 0; j < len; i++, j += 4) {
        output[j] = (unsigned char)(input[i] & 0xff);
        output[j + 1] = (unsigned char)((input[i] >> 8) & 0xff);
        output[j + 2] = (unsigned char)((input[i] >> 16) & 0xff);
        output[j + 3] = (unsigned char)((input[i] >> 24) & 0xff);
    }
}

/* Decodes input (unsigned char) into output (uint32_t). Assumes len is a multiple of 4. */
void MD5_Decode(uint32_t *output, const unsigned char *input, unsigned int len) {
    unsigned int i, j;

    for (i = 0, j = 0; j < len; i++, j += 4) {
        output[i] = ((uint32_t)input[j]) | (((uint32_t)input[j + 1]) << 8) |
            (((uint32_t)input[j + 2]) << 16) | (((uint32_t)input[j + 3]) << 24);
    }
}

/* MD5 hash function */
void MD5_Hash(const unsigned char *input, unsigned int inputLen, unsigned char *digest) {
    MD5_CTX ctx;

    MD5_Init(&ctx);
    MD5_Update(&ctx, input, inputLen);
    MD5_Final(&ctx, digest);
}

